I'm in the process of recording voices for my project. I went down to the local university (which i attend, it may be harder to wander around without the proper ID). I wandered around the drama block asking for permission to talk to the classes and i put some flyers around and held interviews/auditions. All the students were happy for the chance to do something outside of their classes for free. It can't hurt to offer money though but make sure you do auditions because you don't want to get lumbered with someone who is only doing it for the money or aren't as good as they think they are.
I've heard of people doing it all over the internet but you can't really direct your actors or control the recording properly. If its definitely going to be published then you might consider hiring out a floating room somewhere, i've got access at the uni for this (outside of class hours obviously) and it has helped a great deal with controlling the quality of the recordings and i can direct my actors perfectly. They are all following rough previs and they all have a copy of the script to keep.
